Hello again Casey,
Adding your own camera directly inside Substance 3D Painter would be a great feature, and let me consider your message as a suggestion for the team.
With that being said, you can already import cameras with your 3D model when creating a new project.
And if you need to add a new camera in your project, you can even update your file with the Project Configuration window.
I hope this workaround will be helpful.
Best regards,